I always have felt its out-of-character for Lois to extend her lifespan artificially. She gets to live for eons just because she happens to be married to Superman? She doesn't put herself on that kind of pedestal. She's a mortal human being. A proud mortal human being. I have no trouble buying the idea of magical ageless serums in a lore such as the DCU, don't get me wrong, I'm not claiming the very concept goes too far or defies suspension of disbelief. But the character I grew up reading wouldn't utilize them. In my head Lois ages and dies, because that is life, that is the natural order of her species, and its a lot Lois and he will have accepted will eventually happen long before it does. No one lives forever. Not even Superman, its just both a blessing and a curse that his lifespan defies that of human beings by quite a bit.
I have no problem with people who disagree, anything we ever get from such time periods is always somewhere in the "imaginary story" realm anyway so anyone is free to believe what they want there. Those can and often are utilized to be as out there as can be because it can be afforded, as it never really has to count toward an ongoing continuity. This has always been my personal take, though.